External SSD on Imac

Hi there, first post this so please bear with me, just bought a fantastic 2010 i3 27" imac 8gb ram on ebay with 15 months applecare thrown in £800!, so i want to keep the warranty in tact...

Now I've been thinking of attaching an 'external' SSD I know it's better to have it in the imac but I don't want to void the applecare, so the questions i have please are:

1) should I boot from it (should I install lion directly and is this easy enough)
2) should I also boot all apps from it (Cs6)
3) What minimum size (for cost) would be good)
4) no thunderbolt so whats the next best connection

My sister will be running her boot drive from an external FW400 drive as her SATA cable or card has bit the dust. It will be somewhat slower, but with what she uses it for, she won't even notice. FW800 should have some benefit over the FW400, but unless you are a power user, it shouldn't make that much of a difference.

I ran my wife's 2011 Mac Mini off a 240GB SSD connected through FW 800, and it was significantly faster than running off the internal 750GB 7200 RPM drive. Apps and files opened instantly. Open and Save times in PhotoShop dropped in half. Just make sure you get a self-powered enclosure for the SSD. The Mac Mini woke up very grumpy when I ran the SSD bus-powered.

That's interesting, Dennis, because it is exactly the opposite of my experience. Starting the computer and launching apps is disk I/O intensive and this happened much quicker using the SSD in a FW 800 enclosure. Platter-based drives slow to a crawl when reading small files. SSDs do not get nearly as slow. When your drive is reading well below FW 800 speeds the SSD will give you a performance boost even in an external enclosure.

My next trick will be getting a LaCie eSATA Thunderbolt hub and connecting my SSD to my iMac through that.

That makes sense. My iMac is much faster opening apps and files than my wife's Mac Mini even though both have 7200 RPM drives. The Mini, of course, uses 2.5-inch drives which are slower than 3.5-inch drives. USB 2 is painfully slow when used as a boot drive. That's why I bought a FW enclosure for my 2.5 inch drives. I haven't tested USB 3 yet but the speed should be much faster than FW 800.